TOOL · CALCULATOR
Compound interest calculator
Enter the initial amount, monthly deposit and rate, and the final balance shows up instantly — along with total invested, total interest and the month-by-month or year-by-year breakdown.
Final amount
Total invested: —
Total interest: —
Processed in your browser — your files never leave your computer.
How it works
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Fill in amount and deposit
Type the "Initial amount" — what you start with — and, if you save every month, the "Monthly deposit (optional)". Comma or dot as decimal separator, either works.
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Enter the rate and the period
Type the "Interest rate (%)" and pick whether it is per month or per year — for yearly rates, the tool converts and shows the equivalent monthly rate. Then enter the "Period", in months or years.
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Read the result
The "Final amount" appears highlighted, with total invested and total interest right below. Want the journey? Open the month-by-month breakdown (up to 24 months) or year by year.
Frequently asked questions
What is compound interest?
Interest that earns interest. Example: $1,000 at 1% per month becomes $1,010 after the first month. In the second, the 1% applies to the $1,010 — and so on. It looks small, but over long periods that snowball makes a huge difference: that is why they say time is interest's best friend.
Is my rate per month or per year?
Savings products usually advertise yearly rates (e.g. "12% p.a."); some accounts show monthly yields. Pick the right option in the selector — choosing "per year", the tool converts properly (compounding, not dividing by 12) and shows the equivalent monthly rate.
When does the monthly deposit enter the math?
At the end of each month, after that month's interest. So the month-1 deposit only starts earning in month 2. It is the most common way to simulate saving every month.
Can I use it for savings accounts or CDs?
You can estimate, using the product's rate. But the result is gross: taxes and fees are not included — and past returns do not guarantee future ones. The tool does the math; where to invest is your call (or your advisor's).
Is there a period limit?
Up to 100 years. Beyond that the simulation turns into science fiction, so the tool warns you and stops there. Negative values are out too — only positive numbers or zero.
Are my values sent anywhere?
No. The math happens in your browser, on your device — no value ever goes to any server. You can even turn off Wi-Fi after the page loads.